EL34 Grid Stopper resistor

[ca7922303]

Just look at the track on the board and tell me if is how I drawled with red. It is a black wire in front I cannot see

Yes, what you've drawn is correct.

[ca7922303]

Or get a better picture perpendicular to the board. If there are wires in front I cannot guess how the tracks looks behind. Same frame but a better angle..just move those black wire a bit to see how the track behind it looks like

[ca7922303]

Judging by you picture the wires are posed in original position. But still you may try to switch the connectors of dark blue and green to the board. Be aware you amp may severe oscillate if I.m wrong, so keep an eye on it to cut the power off quick if happen.

Switched wires and now the only oscillation that occurs is when I push xpand or boost buttons. Red plating is still occuring as before. Good eye catching where I crossed the wires. Thanks.

[catalin gramada]

Ok I see now. Well you tested nothing valuable in principle cause the nfb circuit was not opened. You removed those link between blue/green points but nfb is still injected through those junction I see it now. Too many components to remove. I wonder I'd switching the impedance switch will do a difference, but you have to check. First take off those 100k resistor you just puted. Then measure the resistance between yellow and red points switching the impedance switch in one side than in the other.

[ca7922303]

Ok I see now. Well you tested nothing valuable in principle cause the nfb circuit was not opened. You removed those link between blue/green points but nfb is still injected through those junction I see it now. Too many components to remove. I wonder I'd switching the impedance switch will do a difference, but you have to check. First take off those 100k resistor you just puted. Then measure the resistance between yellow and red points switching the impedance switch in one side than in the other.

Yellow to red points(4.5k ohms).

[catalin gramada]

Your v6 phase inverter is still conected to output jack. If you want to check if oscillations are due to nfb issue you have to disconect it. But there are still 2 components into the link 100k nfb resistor on a side and 1M+100k in the other. You have to broke the circuit where I put the yellow line. Yo may cut the cooper trace and restore then with a wire between soldering points or you have to lift one terminal of each 1M resistor and 100k resistor. Then you will have not nfb injected and see if oscillate in open loop. The ideea is to make it stable without any nfb injected then will build the nfb circuit around.

[catalin gramada]

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[ca7922303]

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Ok, cut the trace, do I need the 100k resistor connected from blue to 16 ohm output jack for testing or anything else needed to test?

[catalin gramada]

No take it out first and power on. Those cooper trace from old blue point to v6 is the trace which inject nfb signal to v6. You should have nothing conected to it for the moment. You may cut exactly where I show you with yellow line than we restore the circuit with a short solid wire from solder joint to solder joint

[ca7922303]

No take it out first and power on. Those cooper trace from old blue point to v6 is the trace which inject nfb signal to v6. You should have nothing conected to it for the moment. You may cut exactly where I show you with yellow line than we restore the circuit with a short solid wire from solder joint to solder joint

Still no oscillation on any channel until xpand or boost is engaged. Red plating occurs on channels still with drive/volume/master volume near 10.

[catalin gramada]

Volume was increased substantially?

[ca7922303]

No take it out first and power on. Those cooper trace from old blue point to v6 is the trace which inject nfb signal to v6. You should have nothing conected to it for the moment. You may cut exactly where I show you with yellow line than we restore the circuit with a short solid wire from solder joint to solder joint

Both of these points are reading(103k ohms).

[ca7922303]

Volume was increased substantially?

I believe so.

[ca7922303]

Could the two(2) orange bias leads and two(2) red HT leads need to be swapped?

[ca7922303]

Volume was increased substantially?

I recently replaced the xpand/boost piggyback switch on the main preamp board. Anything to check there since engaging those switches is still causing oscillation?